The present invention relates to a plasma processing apparatus which performs a predetermined process by generating a plasma with an RF electromagnetic field.
In the manufacture of a semiconductor device, plasma processing apparatuses are used often to perform processes such as formation of an oxide film, crystal growth of a semiconductor layer, etching, and ashing. Among the plasma processing apparatuses, an RF plasma processing apparatus is available which can stably generate a plasma even under a comparatively low pressure. The RF plasma processing apparatus generates a high-density plasma by introducing an RF electromagnetic field into a processing vessel through a planar antenna.
A case wherein the RF plasma processing apparatus is applied to an etching apparatus will be described. FIG. 20 is a view showing the arrangement of an etching apparatus using a conventional RF plasma processing apparatus. FIG. 20 shows the sectional structure of part of the arrangement.
A dielectric plate 113 is horizontally arranged in the upper opening of a cylindrical processing vessel 111. A seal member 112 is disposed at the bonding portion between the processing vessel 111 and dielectric plate 113 so that the hermeticity in the processing vessel 111 is ensured. Vacuum exhausting exhaust ports 114 are formed in the bottom of the processing vessel 111. A gas supply nozzle 116 is formed in the side wall of the processing vessel 111. The processing vessel 111 accommodates a susceptor 122 on which a substrate 121 as an etching target is to be placed. An RF voltage is applied to the susceptor 122 from an RF power supply 126.
A radial antenna 130 is disposed on the dielectric plate 113 to supply a microwave MW into the processing vessel 111 as an RF electromagnetic field. The dielectric plate 113 and radial antenna 130 are covered by a seal material 117.
The radial antenna 130 is formed of two parallel conductive plates 131 and 132 which form a radial waveguide, and a ring member 133 which closes the edges of the conductive plates 131 and 132. The conductive plate 131 constituting the radiation surface of the microwave MW has a large number of slots 134. The radial antenna 130 is connected to a microwave generator 145 through a waveguide 141.
In the etching apparatus with this arrangement, the interior of the processing vessel 111 is set to a predetermined vacuum degree, and after that a gas mixture of, e.g., CF4 and Ar, is supplied from the nozzle 116 under flow rate control. In this state, the microwave generator 145 supplies the microwave MW to the radial antenna 130 through the waveguide 141.
The microwave MW supplied to the radial antenna 130 is radiated from the large number of slots 134 formed in the conductive plate 131 while propagating in the radial waveguide. As the conductive plate 131 is a horizontally arranged flat plate, the microwave MW is radiated in the vertical direction. The microwave MW is transmitted through the dielectric plate 113 and introduced into the processing vessel 111.
The microwave MW introduced into the processing vessel 111 ionizes the gas in the processing vessel 111 to generate a plasma in a space S1 above the substrate 121 as the processing target. At this time, the microwave MW introduced into the processing vessel 111 is not entirely absorbed directly by plasma generation. That microwave MW which is not absorbed but is left repeats reflection in the processing vessel 111 to form a standing wave in a space S2 between the radial antenna 130 and plasma generating space S1. The microwave MW which forms the standing wave is also known to contribute to plasma generation.
The ions of the plasma generated in this manner are extracted by the negative potential of the susceptor 122 and utilized for the etching process.
With the conventional etching apparatus shown in FIG. 20, however, the plasma is not generated uniformly. The plasma generated in the processing vessel 111 with this etching apparatus was observed. Portions 151A and 151B where the plasma is generated at a high density were observed near the center of a plasma generating region 150, as shown in FIG. 5(a) to be mentioned later. Hence, conventionally, on the substrate 121 as the processing target, the etching process progressed faster at a region below a higher-density plasma. This problem of variations in process amount occurred not only in the etching apparatus shown in FIG. 20 but was common among the conventional plasma processing apparatuses.
The present invention has been made to solve the above problems, and has as its object to improve the distribution of the plasma generated by an RF electromagnetic field.